1. Field Of The Invention
This invention relates to a surfactant composition having satisfactory foaming properties, though it comprises a specific nonionic surfactant which has poor foaming properties.
2. Description Of The Background
Nonionic surfactants such as polyoxyethylene surfactants, polyhydric alcohol ester surfactants and ethylene oxide/propylene oxide block copolymer surfactants are generally less irritative to the skin including mucosae. Further, the nonionic surfactants do not ionize over a wide range of pH values ranging from weakly acidic to weakly alkaline, which makes it easy to control the pH of a composition containing these nonionic surfactants. Because of these characteristics, the nonionic surfactants have been employed as emulsifiers or oily stain removers in various products including skin care products, hair care products, kitchen detergents, oral care products, bathing preparations, drugs and cosmetics.
Among the nonionic surfactants, polyoxyethylene nonionic surfactants have been widely employed in particular, since the hydrophilic-hydrophobic balance thereof can be easily controlled by regulating the polyoxyethylene chain length and because they can easily be synthesized.
In general, ester type nonionic surfactants are superior to the corresponding ether surfactants from the viewpoint of biodegradability. Also, the former is less irritative than the latter. Accordingly, ester type surfactants such as those represented by formula (3): EQU R.sup.0 (OCH.sub.2 CH.sub.2).sub.n OH (3)
which have an alkanoyl group (R.sup.0) derived from a higher fatty acid such as lauric acid, which is a lipophilic group of the polyoxyethylene nonionic surfactant, have been widely employed as emulsifiers. Recently, it has been proposed, for example, in JP-A-4-279552 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") to improve the detergency of a nonionic surfactant represented by formula (3) by etherifying its terminal OH group with a methyl group as shown in formula (4): EQU R.sup.0 (OCH.sub.2 CH.sub.2).sub.n OCH.sub.3 ( 4)
wherein R.sub.0 represents an alkanoyl group such as lauroyl. PA1 wherein R represents an alkanoyl or alkenoyl group having from 10 to 18 carbon atoms; R.sup.1 represents alkylene having from 2 to 4 carbon atoms; R.sup.2 represents a lower alkyl group; and n is from 5 to 100 on the average; PA1 wherein R.sup.3 represents an alkanoyl group having from 8 to 16 carbon atoms or an alkenoyl group having from 12 to 22 carbon atoms. PA1 wherein R, R.sup.1 and R.sup.2 have each the same meaning as
However a polyoxyethylene nonionic surfactant of the ester type represented by formula (4), the terminal of which has been etherified with a lower alkyl group such as a methyl group, exhibits poor foaming properties similar to other nonionic surfactants. Thus, there arises the problem that a detergent, for example, a hair shampoo or a body shampoo containing such a nonionic surfactant fails to lather well and thus cannot give a satisfactory feel in use.